THE MAGICIAN HELIUM-4

THE MAGICIAN HELIUM-4

   

-By Keshu Ranjan

- Batch(2k18), Deptt. of Chemical Engg.

- BIT Sindri, Dhanbad

Here, we will be talking about the strangest liquid we had ever seen, A liquid having zero viscosity. In all liquids we observe in our real life has an opposing flow property called as viscosity of fluid. A flowing liquid experiences viscosity that causes it to slow down. But at 2 Kelvin (-271.15 °C), Helium becomes a superfluid with properties unlike any other fluid we can create.

Let’s talk first about Superfluidity,

Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely.

Superfluidity flows from the counterintuitive rules of quantum mechanics. But unlike other quantum stuff, superfluid helium's weird behaviour is visible to the naked eye.

But NEVER & Ever think same about a soft drink spontaneously overflowing its rim or shooting up and out of the straw from which you're trying to drink. There’s nothing like the superfluid Helium-4 in them.

So, you must be in confusion about WHAT THIS HELIUM-4 is??

 Helium-4 (⁴He) is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.

WHAT MAKES HELIUM DIFFERENT??

Helium has its unique ability to remain in liquid state at absolute zero (-459.67 °F, or -273.15 °C), the temperature at which atoms theoretically stop moving. When most liquids are cooled, the slight attraction between atoms in the fluid finally begins to overcome heat vibrations, and the particles settle into a regular order, namely a solid. But helium atoms are so light and weakly drawn to one another that even when ordinary atomic motions have quieted, the atoms jiggle with zero-point motion, a slight momentum imparted by the quantum uncertainty principle. Hence, they never settle into the solid state.

Experiments have proved that superfluid helium is a mixture of two fluids, one normal and one superfluid. As the temperature falls, the superfluid fraction takes up a greater share of the mixture. In the field's gold-standard experiment, researchers measure the ratio of the two fractions by placing a sample in a cylindrical metal container suspended by a wire. When they impart a twist to the wire, the cylinder will rotate one way and then the other. But only the normal fraction will rotate with the cylinder, because of friction between it and the cylinder walls; the superfluid portion cuts right through the normal fluid and remains still. As the superfluid fraction increases, the cylinder rotates faster, as if the cylinder were losing weight (technically, inertia).

HELIUM AS SUPERFLUID

 Superfluid Helium flows without viscosity under a critical velocity of about 20 cm/s.

Helium becomes a liquid at 4K.

But at 2.17K it becomes a superfluid!

It just keeps going!

·        It can leak through cracks far too small for other liquids to fit through.

 ·     It can climb up walls via microscopic films.

 

·        It becomes still at 2.17 Kelvin; thus, all of its atoms attained the same temperature.

FACTS ABOUT HELIUM…

1. Helium was discovered in the Sun’s atmosphere before it was found on Earth.

2. Helium balloons can reach the edge of space. NASA’s Ultra Long Duration Balloons (ULDBs) can lift 6000 lbs to an altitude of 110,000 feet, above 99% of Earth’s atmosphere. ULDBs are huge – 500 feet tall, made of 20 acres of plastic and can carry heavy instruments – to study cosmic rays.

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